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New Jersey U.S. Sen. Robert Menendez employed as an unpaid intern in his Senate office an illegal immigrant who was a registered sex offender, now under arrest by immigration authorities, he confirmed on MSNBC Wednesday. Jonathan Dienst reports. (Published Wednesday, Dec. 12, 2012)

Updated at 8:39 PM EDT on Wednesday, Dec 12, 2012

U.S. Sen. Robert Menendez employed as an unpaid intern in his Senate office an illegal immigrant who was a registered sex offender, now under arrest by immigration authorities, he confirmed on MSNBC Wednesday.

A source familiar with the case told NBC 4 New York that ICE agents were set to pick up the intern weeks before Election Day but were told from the Homeland Security Department to wait until after the election.

Luis Abrahan Sanchez Zavaleta, an 18-year-old immigrant from Peru, was arrested by U.S. Immigration and Customs Enforcement agents in front of his home in New Jersey on Dec. 6. Sanchez, who entered the country on a now-expired visitor visa from Peru, is facing deportation and remains in custody.

Menendez said on MSNBC that the intern was recommended by the school and that his office wouldn't have known about his sex offender status because it would have been when he was a minor.

He was let go "once it came to our attention," Menendez said.

Menendez denied the allegation that the arrest was put off until after the election, as did a DHS spokesman.

"The report is categorically false," said Peter Boogaard. "ICE followed standard process in coordination with its federal partners and local prosecutors before taking appropriate enforcement action."

Menendez, D-N.J., who advocates aggressively for pro-immigration policies, was re-elected in November with 58 percent of the vote. Congressional staffers who work for Menendez were notified about Sanchez's case shortly after the arrest. Sanchez told ICE agents that he worked on immigration issues for the senator.

Online jail records did not indicate whether Sanchez has an attorney. Immigration officials there were relaying a request from the AP to speak with Sanchez in jail.

The prosecutor's office in Hudson County, N.J., said Sanchez was found to have violated the law in 2010 and subsequently required to register as a sex offender. The exact charge was unclear because Sanchez was prosecuted as a juvenile and those court records are not publicly accessible. The prosecutor's office confirmed to AP that Sanchez registered as a sex offender, although his name does not appear on the public registry.

Authorities in Hudson County notified ICE agents in early October that they suspected Sanchez was an illegal immigrant who was a registered sex offender and who may be eligible to be deported.

It was not immediately clear why federal immigration authorities would not have been notified sooner about Sanchez's status.

During discussions about when and where to arrest Sanchez, the U.S. reviewed Sanchez's application for permission to stay in the country as part of President Barack Obama's policy to allow up to 1.7 million young illegal immigrants avoid deportation and get permission to work for up to two years. As a sex offender, he would not have been eligible. U.S. Citizenship and Immigration Services, which oversees the program known as Deferred Action for Childhood Arrivals, notified Sanchez of that shortly before his arrest, one official said.